AS3 KeyboardEvent Multiple Key press?

My question is: How can I retrieve all the keys that were pressed at the time a KeyEven occured.

The keyCode property only stores one Key. This means that, if I was making a game for example and wanted to have it so that if the up key and the left key were pressed it would move up and left at the same time.

I’ve tried extending the keyboardEvent class and storing the keyCodes in an array, but It returns an error.

Here’s my class.

package{
import flash.events.*
public class KeyEvent extends KeyboardEvent{
public static const KEYS_DOWN = “keysdown”;
private var keys:Array;
public function KeyEvent(type:String){
super(type);
keys=new Array()
}
override public function set keyCode(value:uint):void {
keys.push(super.keyCode)
}
override public function get keyCode():Array {
return keys.concat()
}
override public function clone():Event{
return new KeyEvent(type);
}
}
}

Anyone know a good way to do it?